Conventionally, there is an image forming apparatus such as a multi-function peripheral (hereinafter referred to as a “MFP”) and a printer. The image forming apparatus has a developing device accommodating a developer therein. The developing device includes a developing roller. If air enters the developing device due to rotation of the developing roller, the pressure in the developing device increases. As the pressure in the developing device increases, the air containing a toner in the developing device spouts from the developing device. If the air containing the toner spouts from the developing device, the toner scatters outside the developing device and there is a possibility that the functional components such as a charging device become contaminated with the toner.